Systems and methods for optical systems with exit pupil expander

ABSTRACT

Architectures are provided for expanding the exit pupil of systems including one or more waveguides. Various embodiments include a display device including one or more waveguides. One or more physical/optical parameters of the one or more waveguides and/or a wavelength of light input to the waveguide can be varied as the angle at which incoming light is incident on the waveguide varies in order to maintain phase correlation between different beamlets of the output light beam emitted from the one or more waveguides.

INCORPORATION BY REFERENCE

This application is a continuation of U.S. application Ser. No.16/672,175 filed on Nov. 1, 2019 entitled “SYSTEMS AND METHODS FOROPTICAL SYSTEMS WITH EXIT PUPIL EXPANDER,” which is a continuation ofU.S. application Ser. No. 15/710,055 filed on Sep. 20, 2017 entitled“SYSTEMS AND METHODS FOR OPTICAL SYSTEMS WITH EXIT PUPIL EXPANDER,”which claims the priority benefit of U.S. Provisional Patent ApplicationNo. 62/397,759 filed on Sep. 21, 2016 entitled “SYSTEMS AND METHODS FOROPTICAL SYSTEMS WITH EXIT PUPIL EXPANDER.” The applications recitedabove are each incorporated by reference herein in their entirety.

BACKGROUND Field

The present disclosure relates to virtual reality and augmented realityimaging and visualization systems.

Description of the Related Art

Modern computing and display technologies have facilitated thedevelopment of systems for so called “virtual reality” or “augmentedreality” experiences, wherein digitally reproduced images or portionsthereof are presented to a user in a manner wherein they seem to be, ormay be perceived as, real. A virtual reality, or “VR”, scenariotypically involves presentation of digital or virtual image informationwithout transparency to other actual real-world visual input; anaugmented reality, or “AR”, scenario typically involves presentation ofdigital or virtual image information as an augmentation to visualizationof the actual world around the user. For example, referring to FIG. 1,an augmented reality scene 1000 is depicted wherein a user of an ARtechnology sees a real-world park-like setting 1100 featuring people,trees, buildings in the background, and a concrete platform 1120. Inaddition to these items, the user of the AR technology also perceivesthat he “sees” a robot statue 1110 standing upon the real-world platform1120, and a cartoon-like avatar character 1130 flying by which seems tobe a personification of a bumble bee, even though these elements do notexist in the real world. As it turns out, the human visual perceptionsystem is very complex, and producing a VR or AR technology thatfacilitates a comfortable, natural-feeling, rich presentation of virtualimage elements amongst other virtual or real-world imagery elements ischallenging. Systems and methods disclosed herein address variouschallenges related to VR and AR technology.

SUMMARY

An innovative aspect of the subject matter disclosed herein isimplemented in an optical system comprising an image projection system,a waveguide; and a control system. The image projection system isconfigured to emit a coherent beam of light at a plurality ofwavelengths in the visible spectral range. The waveguide comprises afirst edge, a second edge and a pair of reflective surfaces disposedbetween the first and the second edges. The pair of reflective surfacesis separated by a gap having a gap height d. The waveguide comprises amaterial having a refractive index n. The pair of reflective surfaceshas a reflectivity r. The beam emitted from the image projection systemis coupled into the waveguide at an input angle θ. The input light canbe coupled through one of the first or the second edge or through one ofthe reflective surfaces. The control system is configured to vary atleast one parameter selected from the group consisting of: a wavelengthfrom the plurality of wavelengths, the gap height d, the refractiveindex n and the reflectivity r. The variation of the at least oneparameter is correlated with variation in the input angle θ.

In various embodiments of the optical system the image projection systemcan be configured to vary the input angle θ of emitted beam at a scanrate. The control system can be configured to modulate the at least oneparameter at a modulation rate substantially equal to the scan rate. Thecontrol system can be configured to modulate the at least one parameter,the modulation rate configured such that the equation 2nd sin θ=mλ issatisfied for all values of the input angle θ, wherein m is an integerand λ is wavelength of the beam. In various embodiments, the least oneparameter can be a wavelength from the plurality of wavelengths. In someembodiments, the least one parameter can be the gap height d. In variousembodiments, the least one parameter can be the refractive index n. Insome embodiments, the least one parameter can be the reflectivity r. Invarious embodiments, the image projection system can comprise a fiber.In various embodiments, the emitted beam can be collimated. Theplurality of wavelengths can comprise wavelengths in the red, green andblue spectral regions. The waveguide can comprise an acousto-opticmaterial, a piezo-electric material, an electro-optic material or amicro-electro mechanical system (MEMS). The waveguide can be configuredas an exit pupil expander that expands and multiplies the emitted beam.The waveguide can be configured to expand the beam to a spot sizegreater than 1 mm. Various embodiments of the optical system discussedherein can be integrated in an augmented reality (AR) device, a virtualreality (VR) device, a near-to-eye display device, or an eyewearcomprising at least one of: a frame, one or more lenses or ear stems.

An innovative aspect of the subject matter disclosed herein isimplemented in an optical system comprising an image projection system,a plurality of stacked waveguides, and a control system. The imageprojection system is configured to emit a coherent beam of light at aplurality of wavelengths in the visible spectral range. Each waveguideof the plurality of stacked waveguides comprises a first edge, a secondedge and a pair of reflective surfaces disposed between the first andthe second edges. The pair of reflective surfaces is separated by a gaphaving a gap height d. The waveguide comprises a material having arefractive index n. The pair of reflective surfaces has a reflectivityr. The control system is configured to vary at least one parameterselected from the group consisting of: a wavelength from the pluralityof wavelengths, the gap height d, the refractive index n and thereflectivity r. The beam emitted from the image projection system iscoupled into the waveguide at an input angle θ. The input light can becoupled through one of the first or the second edge or through one ofthe reflective surfaces. The variation of the at least one parameter iscorrelated with variation in the input angle θ.

In various embodiments, each waveguide of the plurality of stackedwaveguides can have an associated depth plane. The beam emitted fromeach waveguide can appear to originate from that waveguide's associateddepth plane. The different waveguides from the plurality of stackedwaveguides can have different associated depth planes. Variousembodiments of the optical system discussed above can be integrated inan augmented reality (AR) device, a virtual reality (VR) device, anear-to-eye display device, or an eyewear comprising at least one of: aframe, one or more lenses or ear stems.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Neitherthis summary nor the following detailed description purports to defineor limit the scope of the inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an illustration of an augmented reality scenario withcertain virtual reality objects, and certain actual reality objectsviewed by a person.

FIG. 2 schematically illustrates an example of a wearable displaysystem.

FIG. 3 schematically illustrates aspects of an approach for simulatingthree-dimensional imagery using multiple depth planes.

FIG. 4 schematically illustrates an example of a waveguide stack foroutputting image information to a user.

FIG. 5 shows example exit beams that may be outputted by a waveguide.

FIG. 6 is a schematic diagram showing an optical system including awaveguide apparatus, an optical coupler subsystem to optically couplelight to or from the waveguide apparatus, and a control subsystem, usedin the generation of a multi-focal volumetric display, image, or lightfield.

FIG. 7 illustrates a waveguide receiving an input light beam beingincident on the waveguide at an angle θ and propagating through thewaveguide by multiple total internal reflections.

FIG. 8A-1 illustrates light output from an embodiment of a waveguidereceiving light from an incoherent light source. FIG. 8B-1 illustratesthe point spread function of the light output from the waveguidedepicted in FIG. 8A-1.

FIG. 8A-2 illustrates light output from an embodiment of a waveguidereceiving light from a coherent light source. FIG. 8B-2 illustrates thepoint spread function of the light output from the waveguide depicted inFIG. 8A-2.

FIG. 8A-3 illustrates light output from an embodiment of a waveguidereceiving light from a coherent light source. FIG. 8B-3 illustrates thepoint spread function of the light output from the waveguide depicted inFIG. 8A-3.

FIG. 8C illustrates a light beam with a continuous wavefront having auniform phase that is output from an embodiment of a waveguide thatreceives light from a coherent input light source and wherein theoptical path length difference between the beams that form the outputlight beam is an integral multiple of the wavelength of the incidentlight.

FIG. 9A schematically illustrates a graph that shows the variation ofrefractive index ‘n’ of the waveguide versus cosine of the input angle.

FIG. 9B schematically illustrates a graph that shows the variation ofthe spacing between the reflective surfaces ‘d’ of the waveguide versuscosine of the input angle.

FIG. 9B-1 illustrates an embodiment of a waveguide comprising threelayers, each layer having a variable reflectivity.

FIG. 9C schematically illustrates a graph that shows the variation ofthe wavelength λ of the incident light versus cosine of the input angle.

FIG. 10 illustrates an embodiment of waveguide comprising a plurality ofspatially multiplexed holographic structures that are configured tooutput a phase synchronized beamlet array for light incident at variableincident angles.

The drawings are provided to illustrate certain example embodiments andare not intended to limit the scope of the disclosure. Like numeralsrefer to like parts throughout.

DETAILED DESCRIPTION

Overview

In order for a three-dimensional (3D) display to produce a truesensation of depth, and more specifically, a simulated sensation ofsurface depth, it is desirable for each point in the display's visualfield to generate the accommodative response corresponding to itsvirtual depth. If the accommodative response to a display point does notcorrespond to the virtual depth of that point, as determined by thebinocular depth cues of convergence and stereopsis, the human eye mayexperience an accommodation conflict, resulting in unstable imaging,harmful eye strain, headaches, and, in the absence of accommodationinformation, almost a complete lack of surface depth.

VR and AR experiences can be provided by display systems having displaysin which images corresponding to a plurality of depth planes areprovided to a viewer. The images may be different for each depth plane(e.g., provide slightly different presentations of a scene or object)and may be separately focused by the viewer's eyes, thereby helping toprovide the user with depth cues based on the accommodation of the eyerequired to bring into focus different image features for the scenelocated on different depth plane and/or based on observing differentimage features on different depth planes being out of focus. Asdiscussed elsewhere herein, such depth cues provide credible perceptionsof depth.

FIG. 2 illustrates an example of wearable display system 80. The displaysystem 80 includes a display 62, and various mechanical and electronicmodules and systems to support the functioning of display 62. Thedisplay 62 may be coupled to a frame 64, which is wearable by a displaysystem user, wearer, or viewer 60 and which is configured to positionthe display 62 in front of the eyes of the user 60. In some embodiments,a speaker 66 is coupled to the frame 64 and positioned adjacent the earcanal of the user (in some embodiments, another speaker, not shown, ispositioned adjacent the other ear canal of the user to provide forstereo/shapeable sound control). The display 62 is operatively coupled68, such as by a wired lead or wireless connectivity, to a local dataprocessing module 71 which may be mounted in a variety ofconfigurations, such as fixedly attached to the frame 64, fixedlyattached to a helmet or hat worn by the user, embedded in headphones, orotherwise removably attached to the user 60 (e.g., in a backpack-styleconfiguration, in a belt-coupling style configuration).

The local processing and data module 71 may comprise a hardwareprocessor, as well as digital memory, such as non-volatile memory (e.g.,flash memory), both of which may be utilized to assist in theprocessing, caching, and storage of data. The data may include data a)captured from sensors (which may be, e.g., operatively coupled to theframe 64 or otherwise attached to the user 60), such as image capturedevices (e.g., cameras), microphones, inertial measurement units,accelerometers, compasses, global positioning system (GPS) units, radiodevices, and/or gyroscopes; and/or b) acquired and/or processed usingremote processing module 72 and/or remote data repository 74, possiblyfor passage to the display 62 after such processing or retrieval. Thelocal processing and data module 71 may be operatively coupled bycommunication links 76 and/or 78, such as via wired or wirelesscommunication links, to the remote processing module 72 and/or remotedata repository 74 such that these remote modules are available asresources to the local processing and data module (71). In addition,remote processing module 72 and remote data repository 74 may beoperatively coupled to each other.

In some embodiments, the remote processing module 72 may comprise one ormore processors configured to analyze and process data and/or imageinformation. In some embodiments, the remote data repository 74 maycomprise a digital data storage facility, which may be available throughthe internet or other networking configuration in a “cloud” resourceconfiguration. In some embodiments, all data is stored and allcomputations are performed in the local processing and data module,allowing fully autonomous use from a remote module.

The human visual system is complicated and providing a realisticperception of depth is challenging. Without being limited by theory, itis believed that viewers of an object may perceive the object as beingthree-dimensional due to a combination of vergence and accommodation.Vergence movements (e.g., rotational movements of the pupils toward oraway from each other to converge the lines of sight of the eyes tofixate upon an object) of the two eyes relative to each other areclosely associated with focusing (or “accommodation”) of the lenses ofthe eyes. Under normal conditions, changing the focus of the lenses ofthe eyes, or accommodating the eyes, to change focus from one object toanother object at a different distance will automatically cause amatching change in vergence to the same distance, under a relationshipknown as the “accommodation-vergence reflex.” Likewise, a change invergence will trigger a matching change in accommodation, under normalconditions. Display systems that provide a better match betweenaccommodation and vergence may form more realistic or comfortablesimulations of three-dimensional imagery.

FIG. 3 illustrates aspects of an approach for simulatingthree-dimensional imagery using multiple depth planes. With reference toFIG. 3, objects at various distances from eyes 302 and 304 on the z-axisare accommodated by the eyes 302 and 304 so that those objects are infocus. The eyes 302 and 304 assume particular accommodated states tobring into focus objects at different distances along the z-axis.Consequently, a particular accommodated state may be said to beassociated with a particular one of depth planes 306, with has anassociated focal distance, such that objects or parts of objects in aparticular depth plane are in focus when the eye is in the accommodatedstate for that depth plane. In some embodiments, three-dimensionalimagery may be simulated by providing different presentations of animage for each of the eyes 302 and 304, and also by providing differentpresentations of the image corresponding to each of the depth planes.While shown as being separate for clarity of illustration, it will beappreciated that the fields of view of the eyes 302 and 304 may overlap,for example, as distance along the z-axis increases. In addition, whileshown as flat for ease of illustration, it will be appreciated that thecontours of a depth plane may be curved in physical space, such that allfeatures in a depth plane are in focus with the eye in a particularaccommodated state. Without being limited by theory, it is believed thatthe human eye typically can interpret a finite number of depth planes toprovide depth perception. Consequently, a highly believable simulationof perceived depth may be achieved by providing, to the eye, differentpresentations of an image corresponding to each of these limited numberof depth planes.

Waveguide Stack Assembly

FIG. 4 illustrates an example of a waveguide stack for outputting imageinformation to a user. A display system 100 includes a stack ofwaveguides, or stacked waveguide assembly, 178 that may be utilized toprovide three-dimensional perception to the eye/brain using a pluralityof waveguides 182, 184, 186, 188, 190. In some embodiments, the displaysystem 100 may correspond to system 80 of FIG. 2, with FIG. 4schematically showing some parts of that system 80 in greater detail.For example, in some embodiments, the waveguide assembly 178 may beintegrated into the display 62 of FIG. 2.

With continued reference to FIG. 4, the waveguide assembly 178 may alsoinclude a plurality of features 198, 196, 194, 192 between thewaveguides. In some embodiments, the features 198, 196, 194, 192 may belenses. The waveguides 182, 184, 186, 188, 190 and/or the plurality oflenses 198, 196, 194, 192 may be configured to send image information tothe eye with various levels of wavefront curvature or light raydivergence. Each waveguide level may be associated with a particulardepth plane and may be configured to output image informationcorresponding to that depth plane. Image injection devices 200, 202,204, 206, 208 may be utilized to inject image information into thewaveguides 182, 184, 186, 188, 190, each of which may be configured todistribute incoming light across each respective waveguide, for outputtoward the eye 304. Light exits an output surface of the image injectiondevices 200, 202, 204, 206, 208 and is injected into a correspondinginput edge of the waveguides 182, 184, 186, 188, 190. In someembodiments, a single beam of light (e.g., a collimated beam) may beinjected into each waveguide to output an entire field of clonedcollimated beams that are directed toward the eye 304 at particularangles (and amounts of divergence) corresponding to the depth planeassociated with a particular waveguide.

In some embodiments, the image injection devices 200, 202, 204, 206, 208are discrete displays that each produce image information for injectioninto a corresponding waveguide 182, 184, 186, 188, 190, respectively. Insome other embodiments, the image injection devices 200, 202, 204, 206,208 are the output ends of a single multiplexed display which may, e.g.,pipe image information via one or more optical conduits (such as fiberoptic cables) to each of the image injection devices 200, 202, 204, 206,208.

A controller 210 controls the operation of the stacked waveguideassembly 178 and the image injection devices 200, 202, 204, 206, 208. Insome embodiments, the controller 210 includes programming (e.g.,instructions in a non-transitory computer-readable medium) thatregulates the timing and provision of image information to thewaveguides 182, 184, 186, 188, 190. In some embodiments, the controllermay be a single integral device, or a distributed system connected bywired or wireless communication channels. The controller 210 may be partof the processing modules 71 or 72 (illustrated in FIG. 2) in someembodiments.

The waveguides 182, 184, 186, 188, 190 may be configured to propagatelight within each respective waveguide by total internal reflection(TIR). The waveguides 182, 184, 186, 188, 190 may each be planar or haveanother shape (e.g., curved), with major top and bottom surfaces andedges extending between those major top and bottom surfaces. In theillustrated configuration, the waveguides 182, 184, 186, 188, 190 mayeach include light extracting optical elements 282, 284, 286, 288, 290that are configured to extract light out of a waveguide by redirectingthe light, propagating within each respective waveguide, out of thewaveguide to output image information to the eye 304. Extracted lightmay also be referred to as outcoupled light, and light extractingoptical elements may also be referred to as outcoupling opticalelements. An extracted beam of light is outputted by the waveguide atlocations at which the light propagating in the waveguide strikes alight redirecting element. The light extracting optical elements 82,284, 286, 288, 290 may, for example, be reflective and/or diffractiveoptical features. While illustrated disposed at the bottom majorsurfaces of the waveguides 182, 184, 186, 188, 190 for ease ofdescription and drawing clarity, in some embodiments, the lightextracting optical elements 282, 284, 286, 288, 290 may be disposed atthe top and/or bottom major surfaces, and/or may be disposed directly inthe volume of the waveguides 182, 184, 186, 188, 190. In someembodiments, the light extracting optical elements 282, 284, 286, 288,290 may be formed in a layer of material that is attached to atransparent substrate to form the waveguides 182, 184, 186, 188, 190. Insome other embodiments, the waveguides 182, 184, 186, 188, 190 may be amonolithic piece of material and the light extracting optical elements282, 284, 286, 288, 290 may be formed on a surface and/or in theinterior of that piece of material.

With continued reference to FIG. 4, as discussed herein, each waveguide182, 184, 186, 188, 190 is configured to output light to form an imagecorresponding to a particular depth plane. For example, the waveguide182 nearest the eye may be configured to deliver collimated light, asinjected into such waveguide 182, to the eye 304. The collimated lightmay be representative of the optical infinity focal plane. The nextwaveguide up 184 may be configured to send out collimated light whichpasses through the first lens 192 (e.g., a negative lens) before it canreach the eye 304. First lens 192 may be configured to create a slightconvex wavefront curvature so that the eye/brain interprets light comingfrom that next waveguide up 184 as coming from a first focal planecloser inward toward the eye 304 from optical infinity. Similarly, thethird up waveguide 186 passes its output light through both the firstlens 192 and second lens 194 before reaching the eye 304. The combinedoptical power of the first and second lenses 192 and 194 may beconfigured to create another incremental amount of wavefront curvatureso that the eye/brain interprets light coming from the third waveguide186 as coming from a second focal plane that is even closer inwardtoward the person from optical infinity than was light from the nextwaveguide up 184.

The other waveguide layers (e.g., waveguides 188, 190) and lenses (e.g.,lenses 196, 198) are similarly configured, with the highest waveguide190 in the stack sending its output through all of the lenses between itand the eye for an aggregate focal power representative of the closestfocal plane to the person. To compensate for the stack of lenses 198,196, 194, 192 when viewing/interpreting light coming from the world 144on the other side of the stacked waveguide assembly 178, a compensatinglens layer 180 may be disposed at the top of the stack to compensate forthe aggregate power of the lens stack 198, 196, 194, 192 below. Such aconfiguration provides as many perceived focal planes as there areavailable waveguide/lens pairings. Both the light extracting opticalelements of the waveguides and the focusing aspects of the lenses may bestatic (e.g., not dynamic or electro-active). In some alternativeembodiments, either or both may be dynamic using electro-activefeatures.

With continued reference to FIG. 4, the light extracting opticalelements 282, 284, 286, 288, 290 may be configured to both redirectlight out of their respective waveguides and to output this light withthe appropriate amount of divergence or collimation for a particulardepth plane associated with the waveguide. As a result, waveguideshaving different associated depth planes may have differentconfigurations of light extracting optical elements, which output lightwith a different amount of divergence depending on the associated depthplane. In some embodiments, as discussed herein, the light extractingoptical elements 282, 284, 286, 288, 290 may be volumetric or surfacefeatures, which may be configured to output light at specific angles.For example, the light extracting optical elements 282, 284, 286, 288,290 may be volume holograms, surface holograms, and/or diffractiongratings. Light extracting optical elements, such as diffractiongratings, are described in U.S. Patent Publication No. 2015/0178939,published Jun. 25, 2015, which is incorporated by reference herein inits entirety. In some embodiments, the features 198, 196, 194, 192 maynot be lenses. Rather, they may simply be spacers (e.g., cladding layersand/or structures for forming air gaps).

In some embodiments, the light extracting optical elements 282, 284,286, 288, 290 are diffractive features that form a diffraction pattern,or “diffractive optical element” (also referred to herein as a “DOE”).Preferably, the DOEs have a relatively low diffraction efficiency sothat only a portion of the light of the beam is deflected away towardthe eye 304 with each intersection of the DOE, while the rest continuesto move through a waveguide via total internal reflection. The lightcarrying the image information is thus divided into a number of relatedexit beams that exit the waveguide at a multiplicity of locations andthe result is a fairly uniform pattern of exit emission toward the eye304 for this particular collimated beam bouncing around within awaveguide.

In some embodiments, one or more DOEs may be switchable between “on”states in which they actively diffract, and “off” states in which theydo not significantly diffract. For instance, a switchable DOE maycomprise a layer of polymer dispersed liquid crystal, in whichmicrodroplets comprise a diffraction pattern in a host medium, and therefractive index of the microdroplets can be switched to substantiallymatch the refractive index of the host material (in which case thepattern does not appreciably diffract incident light) or themicrodroplet can be switched to an index that does not match that of thehost medium (in which case the pattern actively diffracts incidentlight).

In some embodiments, the number and distribution of depth planes and/ordepth of field may be varied dynamically based on the pupil sizes and/ororientations of the eyes of the viewer. In some embodiments, a camera500 (e.g., a digital camera) may be used to capture images of the eye304 to determine the size and/or orientation of the pupil of the eye304. The camera 500 can be used to obtain images for use in determiningthe direction the wearer 60 is looking (e.g., eye pose) or for biometricidentification of the wearer (e.g., via iris identification). In someembodiments, the camera 500 may be attached to the frame 64 (asillustrated in FIG. 2) and may be in electrical communication with theprocessing modules 71 and/or 72, which may process image informationfrom the camera 500 to determine, e.g., the pupil diameters and/ororientations of the eyes of the user 60. In some embodiments, one camera500 may be utilized for each eye, to separately determine the pupil sizeand/or orientation of each eye, thereby allowing the presentation ofimage information to each eye to be dynamically tailored to that eye. Insome other embodiments, the pupil diameter and/or orientation of only asingle eye 304 (e.g., using only a single camera 500 per pair of eyes)is determined and assumed to be similar for both eyes of the viewer 60.

For example, depth of field may change inversely with a viewer's pupilsize. As a result, as the sizes of the pupils of the viewer's eyesdecrease, the depth of field increases such that one plane notdiscernible because the location of that plane is beyond the depth offocus of the eye may become discernible and appear more in focus withreduction of pupil size and commensurate increase in depth of field.Likewise, the number of spaced apart depth planes used to presentdifferent images to the viewer may be decreased with decreased pupilsize. For example, a viewer may not be able to clearly perceive thedetails of both a first depth plane and a second depth plane at onepupil size without adjusting the accommodation of the eye away from onedepth plane and to the other depth plane. These two depth planes may,however, be sufficiently in focus at the same time to the user atanother pupil size without changing accommodation.

In some embodiments, the display system may vary the number ofwaveguides receiving image information based upon determinations ofpupil size and/or orientation, or upon receiving electrical signalsindicative of particular pupil sizes and/or orientations. For example,if the user's eyes are unable to distinguish between two depth planesassociated with two waveguides, then the controller 210 may beconfigured or programmed to cease providing image information to one ofthese waveguides. Advantageously, this may reduce the processing burdenon the system, thereby increasing the responsiveness of the system. Inembodiments in which the DOEs for a waveguide are switchable between onand off states, the DOEs may be switched to the off state when thewaveguide does receive image information.

In some embodiments, it may be desirable to have an exit beam meet thecondition of having a diameter that is less than the diameter of the eyeof a viewer. However, meeting this condition may be challenging in viewof the variability in size of the viewer's pupils. In some embodiments,this condition is met over a wide range of pupil sizes by varying thesize of the exit beam in response to determinations of the size of theviewer's pupil. For example, as the pupil size decreases, the size ofthe exit beam may also decrease. In some embodiments, the exit beam sizemay be varied using a variable aperture.

FIG. 5 shows an example of exit beams outputted by a waveguide. Onewaveguide is illustrated, but it will be appreciated that otherwaveguides in the waveguide assembly 178 may function similarly, wherethe waveguide assembly 178 includes multiple waveguides. Light 400 isinjected into the waveguide 182 at the input edge 382 of the waveguide182 and propagates within the waveguide 182 by TIR. At points where thelight 400 impinges on the DOE 282, a portion of the light exits thewaveguide as exit beams 402. The exit beams 402 are illustrated assubstantially parallel but they may also be redirected to propagate tothe eye 304 at an angle (e.g., forming divergent exit beams), dependingon the depth plane associated with the waveguide 182. It will beappreciated that substantially parallel exit beams may be indicative ofa waveguide with light extracting optical elements that outcouple lightto form images that appear to be set on a depth plane at a largedistance (e.g., optical infinity) from the eye 304. Other waveguides orother sets of light extracting optical elements may output an exit beampattern that is more divergent, which would require the eye 304 toaccommodate to a closer distance to bring it into focus on the retinaand would be interpreted by the brain as light from a distance closer tothe eye 304 than optical infinity.

FIG. 6 shows another example of the optical display system 100 includinga waveguide apparatus, an optical coupler subsystem to optically couplelight to or from the waveguide apparatus, and a control subsystem. Theoptical system 100 can be used to generate a multi-focal volumetric,image, or light field. The optical system can include one or moreprimary planar waveguides 1 (only one is shown in FIG. 6) and one ormore DOEs 2 associated with each of at least some of the primarywaveguides 1. The planar waveguides 1 can be similar to the waveguides182, 184, 186, 188, 190 discussed with reference to FIG. 4. The opticalsystem may employ a distribution waveguide apparatus, to relay lightalong a first axis (vertical or Y-axis in view of FIG. 6). In variousembodiments, the distribution waveguide apparatus may be configured toexpand the light's effective exit pupil along the first axis (e.g.,Y-axis) and/or expand the area in which a viewer can position his eyesto view the optical display system (also referred to herein as eyebox).The distribution waveguide apparatus, may, for example include adistribution planar waveguide 3 and at least one DOE 4 (illustrated bydouble dash-dot line) associated with the distribution planar waveguide3. The distribution planar waveguide 3 may be similar or identical in atleast some respects to the primary planar waveguide 1, having adifferent orientation therefrom. Likewise, the at least one DOE 4 may besimilar or identical in at least some respects to the DOE 2. Forexample, the distribution planar waveguide 3 and/or DOE 4 may becomprised of the same materials as the primary planar waveguide 1 and/orDOE 2, respectively. Embodiments of the optical display system 100 shownin FIG. 4 or 6 can be integrated into the wearable display system 80shown in FIG. 2.

The relayed and exit-pupil expanded light is optically coupled from thedistribution waveguide apparatus into the one or more primary planarwaveguides 1. The primary planar waveguide 1 relays light along a secondaxis, preferably orthogonal to first axis, (e.g., horizontal or X-axisin view of FIG. 6). Notably, the second axis can be a non-orthogonalaxis to the first axis. In various embodiments, the primary planarwaveguide 1 can be configured to expand the light's effective exit pupilalong the second axis (e.g., X-axis) and/or expand the eyebox fromwithin which a viewer can view the optical display system. For example,the distribution planar waveguide 3 can relay and expand light along thevertical or Y-axis, and pass that light to the primary planar waveguide1 which relays and expands light along the horizontal or X-axis.

The optical system may include one or more sources of colored light(e.g., red, green, and blue laser light) 110 which may be opticallycoupled into a proximal end of a single mode optical fiber 9. A distalend of the optical fiber 9 may be threaded or received through a hollowtube 8 of piezoelectric material. The distal end protrudes from the tube8 as fixed-free flexible cantilever 7. The piezoelectric tube 8 can beassociated with 4 quadrant electrodes (not illustrated). The electrodesmay, for example, be plated on the outside, outer surface or outerperiphery or diameter of the tube 8. A core electrode (not illustrated)is also located in a core, center, inner periphery or inner diameter ofthe tube 8.

Drive electronics 12, for example electrically coupled via wires 10,drive opposing pairs of electrodes to bend the piezoelectric tube 8 intwo axes independently. The protruding distal tip of the optical fiber 7has mechanical modes of resonance. The frequencies of resonance candepend upon a diameter, length, and material properties of the opticalfiber 7. By vibrating the piezoelectric tube 8 near a first mode ofmechanical resonance of the fiber cantilever 7, the fiber cantilever 7is caused to vibrate, and can sweep through large deflections.

By stimulating resonant vibration in two axes, the tip of the fibercantilever 7 is scanned biaxially in an area filling two dimensional(2D) scan. By modulating an intensity of light source(s) 11 in synchronywith the scan of the fiber cantilever 7, light emerging from the fibercantilever 7 forms an image. Descriptions of such a set up are providedin U.S. Patent Publication No. 2014/0003762, which is incorporated byreference herein in its entirety.

A component 6 of an optical coupler subsystem collimates the lightemerging from the scanning fiber cantilever 7. The collimated light isreflected by mirrored surface 5 into the narrow distribution planarwaveguide 3 which contains the at least one diffractive optical element(DOE) 4. The collimated light propagates vertically (relative to theview of FIG. 6) along the distribution planar waveguide 3 by totalinternal reflection, and in doing so repeatedly intersects with the DOE4. The DOE 4 preferably has a low diffraction efficiency. This causes afraction (e.g., 10%) of the light to be diffracted toward an edge of thelarger primary planar waveguide 1 at each point of intersection with theDOE 4, and a fraction of the light to continue on its originaltrajectory down the length of the distribution planar waveguide 3 viaTIR.

At each point of intersection with the DOE 4, additional light isdiffracted toward the entrance of the primary waveguide 1. By dividingthe incoming light into multiple outcoupled sets, the exit pupil of thelight can be expanded vertically by the DOE 4 in the distribution planarwaveguide 3 and/or the eyebox can be expanded. This vertically expandedlight coupled out of distribution planar waveguide 3 enters the edge ofthe primary planar waveguide 1.

Light entering primary waveguide 1 propagates horizontally (relative tothe view of FIG. 6) along the primary waveguide 1 via TIR. As the lightintersects with DOE 2 at multiple points as it propagates horizontallyalong at least a portion of the length of the primary waveguide 1 viaTIR. The DOE 2 may advantageously be designed or configured to have aphase profile that is a summation of a linear diffraction pattern and aradially symmetric diffractive pattern, to produce both deflection andfocusing of the light. The DOE 2 may advantageously have a lowdiffraction efficiency (e.g., 10%), so that only a portion of the lightof the beam is deflected toward the eye of the viewer with eachintersection of the DOE 2 while the rest of the light continues topropagate through the waveguide 1 via TIR.

At each point of intersection between the propagating light and the DOE2, a fraction of the light is diffracted toward the an exit surface ofthe primary waveguide 1 allowing the light to escape the TIR, and emergefrom the exit surface of the primary waveguide 1. In some embodiments,the radially symmetric diffraction pattern of the DOE 2 additionallyimparts a divergence to the diffracted light such that it appears tooriginate from a focal depth thereby shaping the light wavefront (e.g.,imparting a curvature) of the individual beam as well as steering thebeam at an angle that matches the designed focal depth.

Accordingly, these different pathways can cause the light to be coupledout of the primary planar waveguide 1 by a multiplicity of DOEs 2 atdifferent angles, focal depths, and/or yielding different fill patternsat the exit pupil. Different fill patterns at the exit pupil can bebeneficially used to create a light field display with multiple depthplanes. Each layer in the waveguide assembly or a set of layers (e.g., 3layers) in the stack may be employed to generate a respective color(e.g., red, blue, green). Thus, for example, a first set of three layersmay be employed to respectively produce red, blue and green light at afirst focal depth. A second set of three layers may be employed torespectively produce red, blue and green light at a second focal depth.Multiple sets may be employed to generate a full 3D or 4D color imagelight field with various focal depths.

Other Components of AR Systems

In many implementations, the AR system may include other components inaddition to the wearable display system 80 (or optical systems 100). TheAR devices may, for example, include one or more haptic devices orcomponents. The haptic device(s) or component(s) may be operable toprovide a tactile sensation to a user. For example, the haptic device(s)or component(s) may provide a tactile sensation of pressure and/ortexture when touching virtual content (e.g., virtual objects, virtualtools, other virtual constructs). The tactile sensation may replicate afeel of a physical object which a virtual object represents, or mayreplicate a feel of an imagined object or character (e.g., a dragon)which the virtual content represents. In some implementations, hapticdevices or components may be worn by the user (e.g., a user wearableglove). In some implementations, haptic devices or components may beheld by the user.

The AR system may, for example, include one or more physical objectswhich are manipulable by the user to allow input or interaction with theAR system. These physical objects are referred to herein as totems. Sometotems may take the form of inanimate objects, for example a piece ofmetal or plastic, a wall, a surface of table. Alternatively, some totemsmay take the form of animate objects, for example a hand of the user. Asdescribed herein, the totems may not actually have any physical inputstructures (e.g., keys, triggers, joystick, trackball, rocker switch).Instead, the totem may simply provide a physical surface, and the ARsystem may render a user interface so as to appear to a user to be onone or more surfaces of the totem. For example, the AR system may renderan image of a computer keyboard and trackpad to appear to reside on oneor more surfaces of a totem. For instance, the AR system may render avirtual computer keyboard and virtual trackpad to appear on a surface ofa thin rectangular plate of aluminum which serves as a totem. Therectangular plate does not itself have any physical keys or trackpad orsensors. However, the AR system may detect user manipulation orinteraction or touches with the rectangular plate as selections orinputs made via the virtual keyboard and/or virtual trackpad.

Examples of haptic devices and totems usable with the AR devices, HMD,and display systems of the present disclosure are described in U.S.Patent Publication No. 2015/0016777, which is incorporated by referenceherein in its entirety.

Optical Systems with Exit Pupil Expander

An optical system (e.g., wearable display system 80 or the opticalsystem 100) comprising a waveguide (e.g., planar waveguide 1) that isconfigured to output incoupled light propagating through the waveguidevia total internal reflection can be associated with an exit pupilconfigured such that light rays that exit the system through the exitpupil can be viewed by a user. An exit pupil larger than the pupil sizeof the user's eyes wastes some light, but allows for some tolerance inside-to-side movement of the user's head or eye. The optical system canalso be associated with an eyebox which corresponds to the volume wherethe user can place his/her eye without sacrificing full field of view(FOV) and/or the full resolution of the optical system.

Various embodiments of optical systems (e.g., wearable display system 80or the optical system 100) can include additional waveguides (e.g., thedistribution waveguide apparatus 3 illustrated in FIG. 6) that areconfigured to increase the size of the light beam that exits the opticalsystem. Increasing the size of the light beam that exits the opticalsystem can advantageously expand the size of the exit pupil of theoptical system. Expanding the size of the exit pupil can be useful whenthe optical system is configured to be directly viewed by a user and/orin near-to-eye display applications. Expanding the size of the exitpupil can also be advantageous in alleviating the strain on eye whenviewing the optical system.

Various embodiments of an optical system (e.g., wearable display system80 or the optical system 100) can comprise a waveguide (e.g., planarwaveguide 1) having two reflective surfaces—a first reflective surfaceand a second reflective surface. An incoming light beam incident on thefirst reflective surface at an angle θ can be coupled into the waveguidesuch that it propagates through the waveguide via total internalreflection at the first and the second reflective surfaces. Eachoccurrence of total internal reflection at the first and the secondreflective surface can be considered to produce a copy of the incominglight beam. Accordingly, multiple copies of the incoming light beam canbe produced as the light beam propagates through the waveguide. Incominglight beam that propagates through the waveguide can be outcoupled outof the waveguide through the second reflective surface. Each copy of theincoupled light beam can be considered to be a kaleidoscopic copy or amirror image of the incoupled light beam. Accordingly, the light that iscoupled out of the second reflective surface of the waveguide can beconsidered to include a beamlet array including a plurality of lightbeams that are copies of the incoupled light beam. Each of the pluralityof light beams can have a beam diameter that is equal to the beamdiameter of the incoupled light beam. Each of the plurality of lightbeams of the beamlet array can appear to originate from a virtual sourcethat is disposed on a side of the reflective surface from which theincoupled light beam is total internally reflected. Accordingly, eachreflective surface of the waveguide produces a set of mirror imagecopies of the input light source that emits the incoming light beam. Theset of mirror image copies appear to be on a side of a respectivereflective surface. This is explained further below with reference toFIG. 7 which illustrates an incoupled light beam 701 being incident on afirst reflective surface 712 b of a waveguide 710 at an angle θ andpropagating through the waveguide 710 by multiple total internalreflections at the first reflective surface 712 b and a secondreflective surface 712 a opposite the first reflective surface 712 b ofthe waveguide 710. Reflected light beams 702, 703, 704, 705 and 706 arereflected from the surface 712 a and/or 712 b at an angle θ with respectto a normal to surface 712 a and/or 712 b. As discussed above, eachreflected beam 702, 703, 704, 705 and 706 can be considered to be a copyof the incoupled light beam 701. A portion of each reflected beam 702,703, 704, 705 and 706 can exit the waveguide 710 through the secondreflective surface 712 a to form a beamlet array including a pluralityof light beams, each light beam in the plurality being a copy of theincoupled light beam. For example, each light beam in the plurality oflight beams can comprise the same image information. In variousembodiments, the portion of each reflected beam 702, 703, 704, 705 and706 in the beamlet array can have a size that is equal to the size ofthe incoupled light beam 701. FIG. 7 illustrates a simplified onedimensional version of the two dimensional beamlet array that isproduced by the optical system (e.g., wearable display system 80 or theoptical system 100) comprising a waveguide (e.g., planar waveguide 1).This two dimensional beamlet array may for example extend along theplane of the first/second reflective surface of the waveguide (e.g.,planar waveguide 1).

A pivotable optical system, such as, for example, a human eye viewingone of the two surfaces of the waveguide 710 (e.g., second reflectivesurface 712 a as illustrated in FIG. 7) can receive the portion of oneor more of the reflected beams 702, 703, 704, 705 and 706 that exit thewaveguide 710. In some such embodiments, the pivotable optical systemcan perceive (i) the incoupled light beam 701 and other reflected beamsthat propagate in a direction parallel to the incoupled beam 701 (e.g.,reflected beams 703 and 705) towards the surface 712 a as being emittedfrom sources (e.g., 701 p, 703 p, 705 p) located on a plane 715perpendicular to the waveguide 710; and (ii) the reflected beams thatpropagate in a direction parallel to the reflected beam 702 (e.g.,reflected beams 704 and 706) towards the surface 712 b as being emittedfrom sources (e.g., 702 p, 704 p, 706 p) located on the plane 715. Themultiple sources 701 p, 702 p, 703 p, 704 p, 705 p and 706 p are mirrorcopies of the input source from which the incoupled light beam isemitted. As illustrated in FIG. 7, sources 701 p, 703 p, and 705 p canbe perceived as being located below the waveguide 710 and sources 702 p,704 p, and 706 p can be perceived as being located above the waveguide710. The sources 701 p, 703 p, and 705 p can be equidistant from eachother. The sources 702 p, 704 p, and 706 p can also be equidistant fromeach other. If the input light source is coherent, the opticalwavefronts that are produced by the plurality of mirrored sources 701 p,702 p, 703 p, 704 p, 705 p and 706 p can interact with one another toproduce an angularly selective interference pattern that can beanalogous to the interference pattern produced by Fabry-Perot etalons,Bragg diffraction gratings, and thin film optics. The distance, s,between consecutive point sources 701 p, 703 p, and 705 p (or 702 p, 704p, and 706 p) can be equal to twice the product of the thickness ‘d’ ofthe waveguide which corresponds to the distance between the surfaces 712a and 712 b and the refractive index ‘n’ of the waveguide 710.Accordingly, the distance, s, between consecutive point sources 701 p,703 p, and 705 p (or 702 p, 704 p, and 706 p) can be calculated usingthe equation s=2nd. As depicted in FIG. 7, the distance, b, between twoadjacent light beams in the beamlet array (also referred to herein asinter-beamlet spacing) that propagate along the same direction and areproduced by the plurality of virtual sources 701 p, 703 p, and 705 p (or702 p, 704 p, and 706 p) is given by the equation b=2nd sin θ, where theangle θ is the angle of incidence of the incoupled light beam. Withoutany loss of generality, light from the input light source can be coupledinto the waveguide 710 through one of the reflective surfaces 712 a or712 b or through one of the edges between the reflective surfaces 712 aor 712 b. In various embodiments, where the incoupled light beam isintroduced into the waveguide 710 by a projector (e.g., a projectionsystem including a fiber cantilever 7 illustrated in FIG. 6), the angleθ can be the scan angle. The optical path length, Γ, between adjacentlight beams of the beamlet array is given by the equation Γ=2nd cos θ.

The point spread function (PSF) of the beamlet array output from thewaveguide can depend on the characteristics of the input light sourcethat outputs the incoupled light beam 701. This is explained herein withreference to FIGS. 8A-1, 8A-2, 8A-3, 8B-1, 8B-2 and 8B-3. FIG. 8A-1illustrates an embodiment of a waveguide 710 that is configured toreceive light output from an incoherent input light source, such as, forexample a LCOS projector. The incoherent input light source thatilluminates the embodiment of the waveguide 710 outputs an incoherentbeam of light having a beam diameter, ‘a’. The beamlet array that exitsthe waveguide 710 includes light beams 801 a, 801 b and 801 c. Since,the input light source is incoherent, the light beams 801 a, 801 b and801 c are mutually incoherent with respect to each other such that aphase relationship between the light beams 801 a, 801 b and 801 cexiting the waveguide cannot be determined. Additionally, for theembodiment illustrated in FIG. 8A-1, the inter-beamlet spacing b betweentwo adjacent light beams (e.g., between 801 a and 801 b or between 801 band beam 801 c) is greater than the beam diameter of each light beam inthe output beamlet array which is substantially the same as the beamdiameter ‘a’, of the input light beam. FIG. 8B-1 illustrates thediffractive pattern 805 a of an individual beam of the beamlet arrayoutput from the embodiment of waveguide 710 illustrated in FIG. 8A-1that receives light from an incoherent input light source. Thediffractive pattern 805 a illustrated in FIG. 8B-1 has a central peakand two sidelobes. Each sidelobe also includes a peak. The width θ_(a),between the maxima of the first sidelobes of the diffractive pattern 805a, can provide a measure of aperture size of the optical systemincluding the waveguide 710 driven by the incoherent light source, isproportional to the ratio λ/a, where λ is the wavelength of the incominglight and ‘a’ is the beam diameter. The point spread function (PSF) forthe beamlet array output from the embodiment of waveguide 710 whichreceives light from an incoherent input light source as illustrated inFIG. 8A-1 is equal to the width θ_(a) of the diffractive pattern 805 aand is equivalent to a wide diffraction envelope that is produced by asingle beam having a beam diameter equal to ‘a’. The PSF represents theimage that an optical system forms of a point source. The PSF of aperfect optical system is an Airy pattern which is made up of a centralspot or peak or a bright region surrounded by concentric rings ofdiminishing intensity. The space between the central spot and successiveconcentric rings has reduced intensity. At large distance from anaperture or pupil having a size d, the angle θ between an axisintersecting the center of the central spot and the region of reducedintensity between the central spot and the first concentric ring isgiven by the equation sin θ=1.22λ/d, where λ is the wavelength of light.Accordingly, as the size of the central spot gets smaller, the pupilsize gets larger. Thus, the Airy pattern (or the PSF) can provide ameasure of the pupil size of an optical system. Without subscribing toany theory a system with a larger pupil size has a narrower PSF.

FIG. 8A-2 illustrates an embodiment of a waveguide 710 that isconfigured to receive light output from a coherent input light source.The coherent input light source that illuminates the embodiment of thewaveguide 710 outputs a coherent beam of light having a beam diameter,a. The beamlet array that exits the waveguide 710 includes light beams802 a, 802 b and 802 c. Since, the input light source is coherent, thelight beams 802 a, 802 b and 802 c are mutually coherent with respect toeach other such that a phase relationship between the light beams 802 a,802 b and 802 c exiting the waveguide is deterministic. Additionally,for the embodiment illustrated in FIG. 8A-2, the inter-beamlet spacing bbetween two adjacent light beams (e.g., between 802 a and 802 b orbetween 802 b and beam 802 c) is greater than the beam diameter of eachlight beam in the output beamlet array which is substantially the sameas the beam diameter ‘a’, of the input light beam. FIG. 8B-2 illustratesthe interference pattern 805 b produced by optical interference betweenthe coherent light beams 802 a, 802 b and 802 c. The interferencepattern 805 b illustrated in FIG. 8B-2 has a central peak and foursidelobes. Each sidelobe also includes a peak. The width Ob, between themaxima of the first sidelobes of the interference pattern 805 b isproportional to the ratio λ/b, where λ is the wavelength of the incominglight and b is the inter-beamlet spacing. The point spread function(PSF) for the beamlet array output from the embodiment of waveguide 710illustrated in FIG. 8A-2 that receives light from a coherent input lightsource is a product of the interference pattern and the diffractiveenvelope of an individual beam of the array which is depicted by thepattern 805 a. Accordingly, the PSF for the beamlet array output fromthe embodiment of waveguide 710 illustrated in FIG. 8A-2 that receiveslight from a coherent input light source corresponds to a diffractionenvelope that is produced by a single beam having a beam diameter equalto ‘a’ angularly filtered by the interference pattern produced by themutual interactions between the coherent beams of the beamlet array. Thespacing between the filter points of the interference pattern producedby the mutual interactions between the coherent beams of the beamletarray is directly proportional to the optical wavelength λ of the beamsand inversely proportional to the inter-beamlet spacing, b. The aperturesize for the beamlet array output from the embodiment of waveguide 710illustrated in FIG. 8A-2 that receives light from a coherent input lightsource can be greater than the aperture size of the optical systemincluding the waveguide 710 driven by an incoherent input light source.

FIG. 8A-3 illustrates an embodiment of a waveguide 710 that isconfigured to receive light output from a coherent input light source.The coherent input light source that illuminates the embodiment of thewaveguide 710 outputs a coherent beam of light having a beam diameter,a. The beamlet array that exits the waveguide 710 is a composite beamthat includes light beams 803 a, 803 b and 803 c. Since, the input lightsource is coherent, the light beams 803 a, 803 b and 803 c are mutuallycoherent with each other such that a phase relationship between thelight beams 803 a, 803 b and 803 c exiting the waveguide isdeterministic. Additionally, for the embodiment illustrated in FIG.8A-3, the inter-beamlet spacing b between two adjacent light beams(e.g., between 803 a and 803 b or between 803 b and beam 803 c) isadjusted such that is it approximately equal to the beam diameter ofeach light beam in the output beamlet array which is substantially thesame as the beam diameter ‘a’, of the input light beam and the opticalpath length difference Γ=2nd cos θ is an integral multiple of thewavelength λ. For this embodiment of the waveguide 710 driven by acoherent light source wherein the angle of incidence and the thicknessand refractive index of the waveguide 710 is an integral multiple of thewavelength λ, the various coherent beams of the beamlet array merge toform a continuous wavefront with a uniform phase. The corresponding PSFwhich is obtained by the product of the interference pattern 805 cillustrated in FIG. 8B-3 and the diffractive envelop of an individualbeam illustrated by the curve 805 a is equivalent to the narrowerdiffraction envelope that is produced by a single beam with diameter ‘A’which is equal to the product of the number of beamlets in the compositebeam and beam diameter ‘a’ of the each individual beam in the beamletarray.

FIG. 8C illustrates a light beam 810 with a continuous wavefront 815having a uniform phase that is output from the embodiment of waveguide710 which receives light from a coherent input light source wherein theoptical path length difference Γ=2nd cos θ is an integral multiple ofthe wavelength λ. As discussed above, the beam diameter, ‘A’ of thelight beam 810 is greater than the beam diameter, ‘a’ of the input lightbeam. In optical systems in which light from a coherent input lightsource is incident at an angle θ on a waveguide having a refractiveindex ‘n’ and thickness ‘d’ such that the optical path length differenceΓ=2nd cos θ is an integral multiple of the wavelength λ of the incidentlight, the waveguide can be configured to function as an exit pupilexpander (EPE). An optical system in which the optical path lengthdifference Γ=2nd cos θ is not an integral multiple of the wavelength λof the incident light need not necessarily expand the exit pupil of thesystem but can instead expand the eyebox of the system. Expanding theeyebox can advantageously increase the tolerance of the system (e.g.,wearable display system 80 or the optical system 100) to side-to-sidemovement of the user's head or eye.

In embodiments of optical systems (e.g., optical system 100) in whichlight from a scanning projector (e.g., a projection system including afiber cantilever 7 illustrated in FIG. 6) is incoupled into a lightguide(e.g., planar waveguide 1), the aperture size of the projector can besmall. For example, the output aperture size of the projector can begreater than or equal to 25 microns and less than or equal to 50microns, greater than or equal to 35 microns and less than or equal to75 microns, greater than or equal to 50 microns and less than or equalto 100 microns, or values therebetween. Various embodiments of suchoptical systems can employ complex lens based optical systems to expandthe input aperture, which corresponds to the aperture size of theprojector. For example, the optical systems employed to expand the exitpupil may be configured to achieve an output aperture that is greaterthan or equal to about 200 microns and less than or equal to about 1 mm,greater than or equal to about 250 microns and less than or equal toabout 950 microns, greater than or equal to about 300 microns and lessthan or equal to about 900 microns, greater than or equal to about 350microns and less than or equal to about 850 microns, greater than orequal to about 400 microns and less than or equal to about 800 microns,greater than or equal to about 450 microns and less than or equal toabout 750 microns, greater than or equal to about 500 microns and lessthan or equal to about 700 microns, greater than or equal to about 550microns and less than or equal to about 650 microns, greater than orequal to about 600 microns and less than or equal to about 650 microns,or values therebetween.

Although, lens based exit pupil expander systems can achieve a desiredoutput aperture size, they can be bulky and heavy making themunpractical to be integrated with near-to-eye display systems. Asdiscussed above waveguides having a refractive index ‘n’ and thickness‘d’ can function as an EPE when the optical path length differencebetween adjacent beams of the beamlet array output from the waveguide,Γ=2nd cos θ is an integral multiple of the wavelength λ of incidentlight can expand the exit pupil. Accordingly, waveguides can provide acompact way of increasing the exit pupil of an optical system withoutcontributing to the weight or bulk.

However, as noted for FIGS. 8A-1 through 8C, optical systems includingwaveguides can function as an exit pupil expander only when the incidentangle at which input light is incoupled into the waveguide, therefractive index ‘n’ and thickness ‘d’ of the waveguide are configuredsuch that the optical path length difference between adjacent beams ofthe beamlet array output from the waveguide, Γ=2nd cos θ is an integralmultiple of the wavelength λ. Light from a scanning projector (e.g., alight source including a fiber cantilever 7 illustrated in FIG. 6) isincident on an optical system that employs a waveguide as an exit pupilexpander, the incident angle θ at which input light is incoupled intothe waveguide varies with the scan angle of the scanning projector whichsweeps out a solid angle Θ corresponding to the field of view (FOV) ofthe optical system. For example, the input angle θ can vary within asolid angle Θ between about 30 degrees to about 50 degrees. If thescanning projector comprises a fiber (e.g., a light source including afiber cantilever 7 illustrated in FIG. 6), then the frequency at whichthe input angle θ varies can be equal to the frequency at which thefiber revolves. In various embodiments of a scanning projectorcomprising a fiber, the fiber can make 11000-30000 revolutions/second.Thus, the input angle θ in such embodiments can vary at a frequencybetween about 0.1 MHz to about 10 MHz.

As the incident angle at which input light is incoupled into thewaveguide varies within the solid angle Θ, the beamlet array output fromthe waveguide is angularly filtered by a discrete two-dimensional (2D)grid of focused spots, as described above with reference to FIGS. 8A-2and 8B-2. The focused spots can correspond to the set of angles thatmeet the phase synchronization condition—the optical path lengthdifference between adjacent beams being an integral multiple of thelight's wavelength. The angular filtration of the beamlet array by thediscrete two-dimensional (2D) grid of focused spots can produceinterference maxima, which correspond to bright, tightly focused pixels,and interference minima, which correspond to dim or blank pixels as theangle of incidence varies within the solid angle Θ if the optical andmechanical properties of the waveguide (e.g., refractive index ‘n’ andthe thickness ‘d’) does not vary correspondingly such that the opticalpath length difference between adjacent beams of the beamelet array isan integral multiple of the wavelength of the light. Thus, the intensityof the beamlet array output from the waveguide can vary intermittentlyas the angle of incidence varies within the solid angle Θ between amaximum brightness and a minimum brightness if the optical andmechanical properties of the waveguide (e.g., refractive index ‘n’ andthe thickness ‘d’) does not vary correspondingly such that the opticalpath length difference between adjacent beams of the beamelet array isan integral multiple of the wavelength of the light. Accordingly, imagesprojected through embodiments of an optical system in which the angle ofincidence varies but the mechanical properties of the waveguide and/orthe wavelength of the incident light remains the same such that theoptical path length difference between adjacent beams of the beameletarray is not an integral multiple of the wavelength of the light for allincident angles can appear as if the images have been sieved by a blackmesh.

In optical systems including a scanning projector with a small aperturesize as a source of optical signal and a waveguide as an exit pupilexpander, it is advantageous to control one or more of the opticaland/or mechanical properties of the display system and/or the input beamto maintain the intensity of projected images at an intensity levelabove a threshold. The optical and/or mechanical properties can includethe spacing between the reflective surfaces of the waveguide (alsoreferred to as the thickness ‘d’), the index of refraction ‘n’ of thewaveguide or the wavelength λ of the input optical signal. The opticaland/or mechanical properties of the display system and/or the input beamcan be controlled to be in synchrony with the variations of the inputbeam's scan angle such that the discrete two-dimensional (2D) grid offocused spots can be angularly shifted in a manner such that every scanangle of the projector will produce a beamlet array that has a compacttightly focused PSF (similar to the PSF depicted in FIG. 8B-3).

The output beam produced by an optical system comprising a waveguidethat splits a scanned input beam into a regular two-dimensional beamletarray including a plurality of light beams can have a beam diameter thatis greater than the beam diameter of individual ones of the plurality oflight beams of the beamlet array when one or more of the physical oroptical properties of the waveguide and/or the wavelength of the scannedinput beam is varied approximately at a frequency of the scan rate. Byvarying one or more of the physical or optical properties of thewaveguide and/or the wavelength of the scanned input beam at a frequencyof the scan rate can advantageously control the relative phase shiftbetween the light beams in the beamlet array such that the output beamhas a continuous wavefront with a uniform phase. Such embodiments of theoptical system can be considered to function as an optical phase arraythat is capable of forming and steering output beams with larger beamdiameters. In such optical systems, the projector's scanning technologycan steer the input beam between the preferred angles of the waveguide'sangular filter grid (which corresponds to the 2D grid of focused spots),and the modulation technologies employed to vary one or more of thephysical or optical properties of the waveguide and/or the wavelength ofthe scanned input beam at the frequency of the scan rate are responsiblefor steering the angular filter grid between the different angles of theinput beam. In various embodiments, the waveguide can be configured suchthat the beamlet array output from the waveguide forms a light beamhaving a continuous wavefront with a uniform phase and a beam diameterthat is larger than the beam diameter of the individual beams in thebeamlet array without dynamically varying (e.g., by utilizing one ormore holographic structures) one or more of the physical or opticalproperties of the waveguide and/or the wavelength of the scanned inputbeam at a frequency of the scan rate. Systems and methods that candynamically or non-dynamically achieve phase synchronization between thevarious light beams of the beamlet array for different scanned angles ofthe input light beam are discussed below.

1. Dynamic Phase Synchronization

A variety of techniques and methods can be used to vary one or more ofthe physical or optical properties of the waveguide and/or thewavelength of the scanned input beam at a frequency of the scan rate todynamically achieve phase synchronization between the various lightbeams of the beamlet array for different scanned angles of the inputlight beam which are discussed below. In various embodiments, theoptical system can comprise a control system that is configured tocontrol one or more of the physical or optical properties of thewaveguide (e.g., refractive index, distance between the reflectivesurfaces of the waveguide) and/or the wavelength of the input beam. Thecontrol system can include feedback loops to continuously maintain phasesynchronization between the individual light beams of the beamlet array.

1.1. Index of Refraction

As discussed above, to maintain phase synchronization between theindividual light beams of the beamlet array the optical path lengthdifference Γ=2nd cos θ should be an integral multiple of the wavelengthλ. Accordingly, if the index of refraction of the material of thewaveguide is varied at a frequency of the scan rate (or at the frequencyat which θ varies) such that the optical path length difference Γ=2ndcos θ is an integral multiple of the wavelength λ for all input anglesθ, then phase synchronization between the individual light beams of thebeamlet array can be maintained for all input angles θ. FIG. 9Aschematically illustrates a graph which shows the variation ofrefractive index ‘n’ of the waveguide versus cosine of the scan angle θ.The points 901 a, 901 b and 901 c of FIG. 9A refer to the refractiveindex value no at scan angles θ_(m), θ_(m+1) and θ_(m+2) at which theterms 2n₀d cos θ_(m), 2n₀d cos θ_(m+1) and 2n₀d cos θ_(m+2) are equal tomλ, (m+1)λ and (m+2)λ respectively, wherein m is an integer. The point901 d of FIG. 9A has a refractive index value of

$\left( \frac{m}{m + 1} \right)$n₀ at scan angle θ_(m+1) such that the term

$2\left( \frac{m}{m + 1} \right)$n₀d cos θ_(m+1) is equal to mλ, wherein m is an integer. The point 901 eof FIG. 9A has a refractive index value of

$\left( \frac{m + 1}{m + 2} \right)$n₀ at scan angle θ_(m+2) such that the term

$2\left( \frac{m + 1}{m + 2} \right)$n₀d cos θ_(m+2) is equal to (m+1)λ, wherein m is an integer. In FIG. 9A,m is considered to have a large value such that

$\left( \frac{m}{m + 1} \right)$n₀ is substantially equal to

$\left( \frac{m + 1}{m + 2} \right)$n₀. Only some of the possible values of refractive index ‘n’ at which2nd cos θ is an integral multiple of the wavelength λ are depicted inFIG. 9A. Other values of refractive index ‘n’ at which 2nd cos θ is anintegral multiple of the wavelength λ are possible. For scan anglesbetween scan angles θ_(m) and θ_(m+1) (or θ_(m+1) and θ_(m+2)) the valueof the refractive index can be changed such that 2nd cos θ remains anintegral multiple of the wavelength λ. For small changes in the value ofthe refractive index ‘n’, the variation of refractive index ‘n’ betweenscan angles θ_(m) and θ_(m+1) (or θ_(m+1) and θ_(m+2)) can be linear asdepicted in FIG. 9A. In various embodiments, the refractive index can bevaried by an amount Δn that is less than or equal to about 25% of a baserefractive index. The base refractive index can correspond to therefractive index value no discussed above. For example, the refractiveindex can be varied by an amount Δn that is less than or equal to about10%, less than or equal to about 15%, less than or equal to about 20% ofthe base refractive index. As discussed above, the variation of therefractive index can be synchronized with the variation in the scanangle θ. As another example, the refractive index can be varied by anamount Δn between approximately 0.001 and about 0.01. The variation ofthe refractive index can be periodic as depicted in FIG. 9A.

Refractive index of the material of the waveguide can be varied by avariety of techniques including but not limited to varying parameters ofan electrical or optical field, varying temperature of the material ofthe waveguide, varying chemical compositions and/or concentrations ofvarious materials comprised in the waveguide, by piezo-optic effects,etc. For example, the waveguide can comprise a crystalline and/or liquidcrystal material whose index of refraction can be varied with theapplication of electric fields via a number of different electro-opticeffects. As another example, the waveguide can comprise a liquidsolution whose index of refraction can be varied by controlling themixing and relative concentrations of its solutes. As another example,the waveguide can comprise a chemically active substrate whose index ofrefraction can be varied by controlling the rate and/or the results ofchemical reactions within the material comprising the waveguide. Forexample, in some embodiments, the rate and/or the results of chemicalreactions within the material comprising the waveguide can be controlledby application of electric field, application of optical field or both.As another example, in some embodiments, the rate and/or the results ofchemical reactions within the material comprising the waveguide can becontrolled by the use of chemical pumps. Changes in optical wavelengthcan also produce changes in the refractive index. Accordingly, invarious embodiments, the change in the refractive index can becorrelated to the wavelength λ of light that is incident on thewaveguide. For example, the wavelength λ of the incident light can varydue to a variety of factors including but not limited to modulation ofthe incident light, non-linearity and/or dispersion of the waveguide.For example, in various embodiments, the wavelength of the incidentlight λ can change by an amount Δλ that is about 1%-10% of thewavelength λ_(optical) of the unmodulated incident light due tomodulation. Accordingly, a controller configured to vary the refractiveindex of the material of the light can be configured to take intoconsideration the change in the wavelength λ of the incident light whencalculating the amount Δn by which refractive index is to be changed. Invarious embodiments, the controller can include a feedback loop that isconfigured to dynamically calculate a change in the wavelength λ of theincident light and calculate the amount Δn by which refractive index isto be changed based on the change in the wavelength λ of the incidentlight such that phase synchronization between the various light beams ofthe beamlet array for different scanned angles of the input light beamcan be achieved.

1.2. Reflector Plane Spacing

Various embodiments of the waveguide can be configured such that thespace (also referred to as thickness of the waveguide) between thereflective surfaces (e.g., reflective surfaces 712 a and 712 b ofwaveguide 710) need not be fixed but instead can be varied. For example,in various embodiments of the waveguide, the space between thereflective surfaces (e.g., reflective surfaces 712 a and 712 b ofwaveguide 710) can be occupied by a fluid or air. The waveguide cancomprise a controller that moves one or both the reflective surfaceswith respect to each other to vary a distance between the reflectivesurfaces and/or a thickness of the space including the fluid or air at afrequency of the scan rate (or at the frequency at which θ varies) suchthat the optical path length difference Γ=2nd cos θ is an integralmultiple of the wavelength λ for all input angles θ. FIG. 9Bschematically illustrates a graph which shows the variation of thespacing between the reflective surfaces ‘d’ of the waveguide versuscosine of the scan angle θ. The points 905 a, 905 b and 905 c of FIG. 9Brefer to the value of the spacing between the reflective surfaces of thewaveguide d₀ at scan angles θ_(m), θ_(m+1) and θ_(m+2) at which theterms 2nd₀ cos θ_(m), 2nd₀ cos θ_(m+1) and 2nd₀ cos θ_(m+2) are equal tomλ, (m+1)λ and (m+2)λ respectively, wherein m is an integer. The spacingbetween the reflective surfaces of the waveguide at point 905 d of FIG.9B is

$\left( \frac{m}{m + 1} \right)$d₀ at scan angle θ_(m+1) such that the term

$2\left( \frac{m}{m + 1} \right)$nd₀ cos θ_(m+1) is equal to mλ, wherein m is an integer. The spacingbetween the reflective surfaces of the waveguide at point 905 e of FIG.9B is

$\left( \frac{m + 1}{m + 2} \right)$d₀ at scan angle θ_(m+2) such that the term

$2\left( \frac{m + 1}{m + 2} \right)$nd₀ cos θ_(m+2) is equal to (m+1)λ, wherein m is an integer. In FIG. 9B,m is considered to have a large value such that

$\left( \frac{m + 1}{m + 2} \right)$d₀ is substantially equal to

$\left( \frac{m}{m + 1} \right)$d₀. Only some of the possible values of the spacing ‘d’ between thereflective surfaces of the waveguide at which 2nd cos θ is an integralmultiple of the wavelength λ are depicted in FIG. 9B. Other values ofthe spacing ‘d’ between the reflective surfaces of the waveguide atwhich 2nd cos θ is an integral multiple of the wavelength λ arepossible. For scan angles between scan angles θ_(m) and θ_(m+1) (orθ_(m+1) and θ_(m+2)) the value of the spacing ‘d’ between the reflectivesurfaces of the waveguide can be changed such that 2nd cos θ remains anintegral multiple of the wavelength λ. For small changes in the value ofthe spacing ‘d’ between the reflective surfaces of the waveguide, thevariation of the spacing ‘d’ between the reflective surfaces of thewaveguide between scan angles θ_(m) and θ_(m+1) (or θ_(m+1) and θ_(m+2))can be linear as depicted in FIG. 9B. The spacing ‘d’ between thereflective surfaces of the waveguide can be varied by an amount Δd thatis less than or equal to about 25% of a base spacing between thereflective surfaces of the waveguide. For example, the spacing ‘d’between the reflective surfaces of the waveguide can be varied by anamount Δd that is less than or equal to about 10%, less than or equal toabout 15%, less than or equal to about 20% of the base spacing betweenthe reflective surfaces of the waveguide. As another example, thespacing ‘d’ between the reflective surfaces of the waveguide can bevaried by an amount Δd less than or equal to about 1 micron. In variousembodiments, the base spacing between the reflective surfaces of thewaveguide can correspond to the spacing do discussed above.

As discussed above, the variation of the spacing ‘d’ between thereflective surfaces of the waveguide can be synchronized with thevariation in the scan angle θ. The variation of the spacing between thereflective surfaces of the waveguide can be periodic as depicted in FIG.9B. The spacing between the reflective surfaces of the waveguide can bechanged by a variety of techniques including but not limited tomechanical methods, electro-mechanical methods, acousto-optic methods,electro-magnetic methods, piezo-electric methods, etc. For example, thewaveguide can be configured as a micro-electro mechanical systems (MEMS)device comprising a pair of reflective surfaces and a controllerconfigured to control the distance between the reflective surfaces. Asanother example, the waveguide can comprise an acousto-optic materialbounded by two surfaces. The two surfaces of the waveguide can beconfigured to be reflective by density variations in the acousto-opticmaterial, that are induced by acoustic standing waves generated by anacoustic driver. In such embodiments, the spacing between the twosurfaces can be varied by changing the frequency of the acoustic driverthat generates the acoustic standing waves.

In another embodiment, the waveguide can comprise a plurality of layersthat are spaced apart from each other. Each of the plurality of layerscan be configured to be switched between a reflective state and atransmissive state. A pair of reflective surfaces with any desiredspacing between them can be obtained by selectively configuring two ofthe plurality of layers to be in a reflective state and configuring theremaining plurality of layers to be in a transmissive state. In suchembodiments, each of the plurality of layers can be switched between thereflective state and the transmissive state using electro-magneticcontrol systems. This is explained in greater detail below withreference to FIG. 9B-1 which depicts a waveguide 907 comprising threelayers 907 a, 907 b and 907 c. The third layer 907 c is disposed betweenthe first layer 907 a and the second layer 907 b. The first layer 907 acan be maintained in a reflective state. By configuring the second layer907 b to be in a transmissive state and the third layer 907 c to be in areflective state, the spacing between the pair of reflective surfaces ofthe waveguide 907 can be selected to be d1. By configuring the secondlayer 907 b to be in a reflective state and the third layer 907 c to bein a transmissive state, the spacing between the pair of reflectivesurfaces of the waveguide 907 can be selected to be d1+d2. In thismanner, the spacing between the reflective surfaces of the waveguide canbe varied. Additional layers can be included in the waveguide to providea greater range of variation in the spacing.

In some embodiments of the waveguide the reflective surfaces cancomprise a piezoelectric material. In such embodiments, the spacingbetween the reflective surfaces can be varied by inducing mechanicalexpansion or contraction of the waveguide via the application of anelectric field.

1.3. Wavelength

Various embodiments of the waveguide can be configured such that thewavelength of the incident light (e.g., light beam 701) can be varied ata frequency of the scan rate (or at the frequency at which θ varies)such that the optical path length difference Γ=2nd cos θ is an integralmultiple of the wavelength λ for all input angles θ. FIG. 9Cschematically illustrates a graph which shows the variation of thewavelength λ of the incident light versus cosine of the scan angle θ.The points 910 a, 910 b and 910 c of FIG. 9C refer to the value of thewavelength λ₀ at scan angles θ_(m), θ_(m+1) and θ_(m+2) at which theterms 2nd cos θ_(m), 2nd cos θ_(m+1) and 2nd cos θ_(m+2) are equal tomλ₀, (m+1)λ₀ and (m+2)λ₀ respectively, wherein m is an integer. Thewavelength λ at point 910 d of FIG. 9C is

$\left( \frac{m + 1}{m} \right)$λ₀ at scan angle θ_(m+1) such that the term 2nd cos θ_(m+1) is equal tomλ₀, wherein m is an integer. The wavelength λ at point 910 e of FIG. 9Cis

$\left( \frac{m + 2}{m + 1} \right)$λ₀ at scan angle θ_(m+2) such that the term

$2\left( \frac{m + 1}{m + 2} \right)$nd₀ cos θ_(m+2) is equal to (m+1)λ₀, wherein m is an integer. In FIG.9C, m is considered to have a large value such that

$\left( \frac{m + 1}{m} \right)$λ₀ is substantially equal to

$\left( \frac{m + 2}{m + 1} \right)$λ₀. Only some of the possible values of the wavelength λ of the incidentlight at which 2ndcos θ is an integral multiple of the wavelength λ aredepicted in FIG. 9C. Other values of the wavelength λ of the incidentlight at which 2nd cos θ is an integral multiple of the wavelength λ arepossible. For scan angles between scan angles θ_(m) and θ_(m+1) (orθ_(m+1) and θ_(m+2)) the value of the wavelength λ of the incident lightcan be changed such that 2nd cos θ remains an integral multiple of thewavelength λ. For small changes in the value of the wavelength λ of theincident light, the variation of the wavelength λ of the incident lightbetween scan angles θ_(m) and θ_(m+1) (or θ_(m+1) and θ_(m+2)) can belinear as depicted in FIG. 9C. The wavelength λ of the incident lightcan be varied by an amount Δλ that is less than or equal to about 25% ofa base wavelength. For example, the wavelength λ of the incident lightcan be varied by an amount Δλ that is less than or equal to about 10%,less than or equal to about 15%, less than or equal to about 20% of thebase wavelength. As another example, wavelength λ of the incident lightcan be varied by an amount Δλ between about 1 nm and about 10 nm. Invarious embodiments, the base wavelength can correspond to thewavelength λ0 discussed above.

As discussed above, the variation of the wavelength λ of the incidentlight can be synchronized with the variation in the scan angle θ. Thevariation of the wavelength λ of the incident light can be periodic asdepicted in FIG. 9C. The wavelength λ of the incident light can bevaried by employing a tunable laser. For example, the optical source(e.g., light/image source 11 of FIG. 6) can include a tunable laser suchas, for example, a distributed feedback (DFB) laser, a distributed Braggreflector (DBR) laser, etc. in which the wavelength λ of the laser canbe varied by application of electrical currents and/or voltages. Asanother example, the wavelength λ of the light output from the opticalsource (e.g., light/image source 11 of FIG. 6) can be varied by varyingthe temperature of the optical source.

As discussed above, changes in optical wavelength can also producechanges in the refractive index. Accordingly, in various embodiments,the change in the wavelength λ of light that is incident on thewaveguide can be correlated to the change in the refractive index ‘n’.For example, a controller configured to vary the wavelength λ ofincident light can be configured to take into consideration the changein the refractive index of the material of the waveguide. In variousembodiments, the controller can include a feedback loop that isconfigured to dynamically calculate a change in the wavelength λ of theincident light based on the change in the refractive index Δn of thewaveguide such that phase synchronization between the various lightbeams of the beamlet array for different scanned angles of the inputlight beam can be achieved.

In general, for dynamic phase synchronization, the angular spacing, inradians, between the angles that meet the phase synchronizationcondition is approximately equal to the light's wavelength, divided bythe width of the waveguide. The angular shift for waveguide widths andbeam diameters of approximately 100 to 1000 microns can be between about0.001 to 0.01 radians (or a percentage change of about 0.1% to 1%). Tomaintain phase synchronization, the angular shift can be compensated bydecreasing the waveguide's index of refraction by an amount in the rangebetween about 0.001 and about 0.01; increasing or decreasing the spacingbetween the reflective surface (or width of the waveguide) byapproximately 1 micron; or by increasing or decreasing the wavelength ofthe incident light in a range between about 1 and about 10 nm.

2. Non-Dynamic Phase Synchronization

Phase synchronization can also be achieved without using any of thedynamic approaches discussed above. For example, the waveguide cancomprise a plurality of holographic structures, each of the plurality ofholographic structures providing a phase synchronized output for eachincident angle. Accordingly, a phase synchronized output can be obtainedas the incident angle of the input beam varies without activelyco-modulating the spacing between the reflective surfaces of thewaveguide, the refractive index of the waveguide or the wavelength ofthe incident light at the scan rate of the input beam.

A first of plurality of holographic structures that provides a phasesynchronized output for a first incident angle can be recorded on athick holographic medium by interfering a first reference beam incidenton the holographic medium from a first side of the holographic medium atthe first incident angle and a second reference beam incident on theholographic medium from a second side of the holographic medium oppositethe first side. The first reference beam can be configured to have thecharacteristics of the light beam output from a scanning projector. Forexample, the first reference beam can be collimated in some embodiments.The first reference beam can have a beam diameter of less than or equalto about 100 microns (e.g., less than or equal to 90 microns, less thanor equal to 80 microns, less than or equal to 70 microns, less than orequal to 60 microns, less than or equal to 50 microns, less than orequal to 40 microns, less than or equal to 30 microns, less than orequal to 25 microns, less than or equal to 20 microns, or valuestherebetween). The second reference beam can be configured to have thecharacteristics of the phase synchronized beamlet array that is outputfrom the waveguide when the first reference beam is incident on thewaveguide at the first incident angle. For example, the second referencebeam can be a collimated beam having a continuous wavefront with auniform phase similar to the beamlet array depicted in FIG. 8A-3 and/orFIG. 8C. The beam diameter of the second reference beam can be greaterthan or equal to about 200 microns and less than or equal to about 10mm. For example, the beam diameter of the second reference beam can begreater than or equal to about 250 microns and less than or equal toabout 950 microns, greater than or equal to about 300 microns and lessthan or equal to about 900 microns, greater than or equal to about 350microns and less than or equal to about 850 microns, greater than orequal to about 400 microns and less than or equal to about 800 microns,greater than or equal to about 450 microns and less than or equal toabout 750 microns, greater than or equal to about 500 microns and lessthan or equal to about 700 microns, greater than or equal to about 550microns and less than or equal to about 650 microns, greater than orequal to about 600 microns and less than or equal to about 650 microns,or values therebetween.

Multiple holographic structures are recorded on the same holographicmedium by varying the incidence angle of the first reference beam. Forexample, the incidence angle of the first reference beam can becontinuously varied between about ±30-degrees. As another example, theincidence angle of the first reference beam can be varied between about±30-degrees in discrete steps that is less than or equal to about 1degree (e.g., less than or equal to 0.9 degrees, less than or equal to0.8 degrees, less than or equal to 0.7 degrees, less than or equal to0.6 degrees, less than or equal to 0.5 degrees, less than or equal to0.4 degrees, less than or equal to 0.3 degrees, less than or equal to0.2 degrees, less than or equal to 0.1 degrees, less than or equal to0.05 degrees, or values therebetween). The angle of incidence of thesecond reference beam can also be varied corresponding to the variationof the incidence angle of the first reference beam.

Accordingly at least one holographic structure is recorded on theholographic medium for each combination of the angle of incidence of thefirst reference beam and the angle of incidence of the second referencebeam. The waveguide comprising a plurality of holographic structuresthat are recorded in this manner can be configured to output a phasesynchronized beamlet array for an input beam incident at the differentangles θ within the solid angle Θ swept by the scanning projector.Furthermore, the diameter of the output beamlet array can be greaterthan the diameter of the input beam. In such embodiments, angularselectivity is built into the waveguide such that it is not necessary todynamically synchronize the phase between the various beams of thebeamlet array as the angle of incidence of the input light is varied.Thus, in such embodiments, one or more parameters of the waveguide(e.g., refractive index, spacing between the reflective surfaces of thewaveguide) and/or the wavelength λ of the incident light need not bevaried at the frequency of the scan rate to achieve phasesynchronization between the various light beams of the beamlet arrayoutput from the waveguide.

FIG. 10 illustrates an embodiment of waveguide 1010 in which the angularselectivity is built into the waveguide such that it is not necessary todynamically synchronize the phase between the various beams of thebeamlet array as the angle of incidence of the input light is varied.The waveguide 1010 comprises a stack of layers 1012 a, 1012 b, 1012 c,1012 d. Each stack of layer can include one or more holographicstructures. The holographic structures can comprise volume hologramsand/or spatially multiplexed Bragg diffraction gratings. In variousembodiments, a plurality of holograms can be superimposed or multiplexedin the volume of the waveguide. In such embodiments, the waveguide neednot comprise a stack of layers. Each holographic structure can beconfigured to output a phase synchronized beamlet array for an inputbeam incident at an angle θ within the solid angle Θ swept by thescanning projector as discussed above. Although, FIG. 10 depicts a phasesynchronized beamlet array 1015 that is output by the waveguide 1010 foran input light beam 1001 that is incident at an angle close to a normalto a surface of the waveguide 1010, the waveguide 1010 can also beconfigured to emit a phase synchronized beamlet array for input beamsincident at angles different from an angle close to a normal to asurface of the waveguide 1010.

Each of the processes, methods, and algorithms described herein and/ordepicted in the attached figures may be embodied in, and fully orpartially automated by, code modules executed by one or more physicalcomputing systems, hardware computer processors, application-specificcircuitry, and/or electronic hardware configured to execute specific andparticular computer instructions. For example, computing systems caninclude general purpose computers (e.g., servers) programmed withspecific computer instructions or special purpose computers, specialpurpose circuitry, and so forth. A code module may be compiled andlinked into an executable program, installed in a dynamic link library,or may be written in an interpreted programming language. In someimplementations, particular operations and methods may be performed bycircuitry that is specific to a given function.

Further, certain implementations of the functionality of the presentdisclosure are sufficiently mathematically, computationally, ortechnically complex that application-specific hardware or one or morephysical computing devices (utilizing appropriate specialized executableinstructions) may be necessary to perform the functionality, forexample, due to the volume or complexity of the calculations involved orto provide results substantially in real-time. For example, a video mayinclude many frames, with each frame having millions of pixels, andspecifically programmed computer hardware is necessary to process thevideo data to provide a desired image processing task or application ina commercially reasonable amount of time.

Code modules or any type of data may be stored on any type ofnon-transitory computer-readable medium, such as physical computerstorage including hard drives, solid state memory, random access memory(RAM), read only memory (ROM), optical disc, volatile or non-volatilestorage, combinations of the same and/or the like. The methods andmodules (or data) may also be transmitted as generated data signals(e.g., as part of a carrier wave or other analog or digital propagatedsignal) on a variety of computer-readable transmission mediums,including wireless-based and wired/cable-based mediums, and may take avariety of forms (e.g., as part of a single or multiplexed analogsignal, or as multiple discrete digital packets or frames). The resultsof the disclosed processes or process steps may be stored, persistentlyor otherwise, in any type of non-transitory, tangible computer storageor may be communicated via a computer-readable transmission medium.

Any processes, blocks, states, steps, or functionalities in flowdiagrams described herein and/or depicted in the attached figures shouldbe understood as potentially representing code modules, segments, orportions of code which include one or more executable instructions forimplementing specific functions (e.g., logical or arithmetical) or stepsin the process. The various processes, blocks, states, steps, orfunctionalities can be combined, rearranged, added to, deleted from,modified, or otherwise changed from the illustrative examples providedherein. In some embodiments, additional or different computing systemsor code modules may perform some or all of the functionalities describedherein. The methods and processes described herein are also not limitedto any particular sequence, and the blocks, steps, or states relatingthereto can be performed in other sequences that are appropriate, forexample, in serial, in parallel, or in some other manner. Tasks orevents may be added to or removed from the disclosed exampleembodiments. Moreover, the separation of various system components inthe implementations described herein is for illustrative purposes andshould not be understood as requiring such separation in allimplementations. It should be understood that the described programcomponents, methods, and systems can generally be integrated together ina single computer product or packaged into multiple computer products.Many implementation variations are possible.

The processes, methods, and systems may be implemented in a network (ordistributed) computing environment. Network environments includeenterprise-wide computer networks, intranets, local area networks (LAN),wide area networks (WAN), personal area networks (PAN), cloud computingnetworks, crowd-sourced computing networks, the Internet, and the WorldWide Web. The network may be a wired or a wireless network or any othertype of communication network.

The systems and methods of the disclosure each have several innovativeaspects, no single one of which is solely responsible or required forthe desirable attributes disclosed herein. The various features andprocesses described above may be used independently of one another, ormay be combined in various ways. All possible combinations andsubcombinations are intended to fall within the scope of thisdisclosure. Various modifications to the implementations described inthis disclosure may be readily apparent to those skilled in the art, andthe generic principles defined herein may be applied to otherimplementations without departing from the spirit or scope of thisdisclosure. Thus, the claims are not intended to be limited to theimplementations shown herein, but are to be accorded the widest scopeconsistent with this disclosure, the principles and the novel featuresdisclosed herein.

Certain features that are described in this specification in the contextof separate implementations also can be implemented in combination in asingle implementation. Conversely, various features that are describedin the context of a single implementation also can be implemented inmultiple implementations separately or in any suitable subcombination.Moreover, although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination. No single feature orgroup of features is necessary or indispensable to each and everyembodiment.

Conditional language used herein, such as, among others, “can,” “could,”“might,” “may,” “e.g.,” and the like, unless specifically statedotherwise, or otherwise understood within the context as used, isgenerally intended to convey that certain embodiments include, whileother embodiments do not include, certain features, elements and/orsteps. Thus, such conditional language is not generally intended toimply that features, elements and/or steps are in any way required forone or more embodiments or that one or more embodiments necessarilyinclude logic for deciding, with or without author input or prompting,whether these features, elements and/or steps are included or are to beperformed in any particular embodiment. The terms “comprising,”“including,” “having,” and the like are synonymous and are usedinclusively, in an open-ended fashion, and do not exclude additionalelements, features, acts, operations, and so forth. Also, the term “or”is used in its inclusive sense (and not in its exclusive sense) so thatwhen used, for example, to connect a list of elements, the term “or”means one, some, or all of the elements in the list. In addition, thearticles “a,” “an,” and “the” as used in this application and theappended claims are to be construed to mean “one or more” or “at leastone” unless specified otherwise.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: A, B, or C” is intended to cover: A, B, C,A and B, A and C, B and C, and A, B, and C. Conjunctive language such asthe phrase “at least one of X, Y and Z,” unless specifically statedotherwise, is otherwise understood with the context as used in generalto convey that an item, term, etc. may be at least one of X, Y or Z.Thus, such conjunctive language is not generally intended to imply thatcertain embodiments require at least one of X, at least one of Y and atleast one of Z to each be present.

Similarly, while operations may be depicted in the drawings in aparticular order, it is to be recognized that such operations need notbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Further, the drawings may schematically depict one more exampleprocesses in the form of a flowchart. However, other operations that arenot depicted can be incorporated in the example methods and processesthat are schematically illustrated. For example, one or more additionaloperations can be performed before, after, simultaneously, or betweenany of the illustrated operations. Additionally, the operations may berearranged or reordered in other implementations. In certaincircumstances, multitasking and parallel processing may be advantageous.Moreover, the separation of various system components in theimplementations described above should not be understood as requiringsuch separation in all implementations, and it should be understood thatthe described program components and systems can generally be integratedtogether in a single software product or packaged into multiple softwareproducts. Additionally, other implementations are within the scope ofthe following claims. In some cases, the actions recited in the claimscan be performed in a different order and still achieve desirableresults.

What is claimed is:
 1. A method comprising: receiving a beam into awaveguide at an input angle θ, the waveguide comprising a first edge, asecond edge and a pair of reflective surfaces disposed between the firstand the second edges, the pair of reflective surfaces separated by a gaphaving a gap height d, the waveguide comprising a material having arefractive index n, and at least one of the pair of reflective surfaceshaving a reflectivity r; and varying at least one parameter selectedfrom the group consisting of: a wavelength from the plurality ofwavelengths, the gap height d, the refractive index n, and thereflectivity r, wherein the variation of the at least one parameter iscorrelated with variation of the input angle θ such that a first valueof the at least one parameter is associated with a first value of theinput angle θ and a second value of the at least one parameter isassociated with a second value of the input angle θ and not with thefirst value of the input angle θ.
 2. The method of claim 1, whereinvarying the at least one parameter comprises varying the input angle θat a scan rate.
 3. The method of claim 1, wherein varying the at leastone parameter comprises varying the at least one parameter at a ratesubstantially equal to a scan rate.
 4. The method of claim 1, whereinthe least one parameter is the wavelength from the plurality ofwavelengths.
 5. The method of claim 1, wherein the least one parameteris the gap height d.
 6. The method of claim 1, wherein the least oneparameter is the refractive index n.
 7. The method of claim 1, whereinthe least one parameter is the reflectivity r.
 8. The method of claim 1,wherein the beam is collimated.
 9. The method of claim 1, wherein thewaveguide comprises an acousto-optic material.
 10. The method of claim1, wherein the waveguide comprises a piezo-electric material.
 11. Themethod of claim 1, wherein the waveguide comprises an electro-opticmaterial.
 12. The method of claim 1, wherein the waveguide comprises amicro-electro mechanical system (MEMS).
 13. The method of claim 1,wherein the waveguide is configured as an exit pupil expander thatexpands and multiplies the emitted beam.
 14. The method of claim 1,wherein the waveguide is configured to expand the beam to a spot sizegreater than 1 mm.
 15. The method of claim 1, wherein the waveguide isintegrated in an augmented reality (AR) device.
 16. The method of claim1, wherein the waveguide is integrated in a near-to-eye display device.17. The method of claim 1, wherein the waveguide is integrated in avirtual reality (VR) device.
 18. The method of claim 1, wherein thewaveguide is integrated in eyewear comprising at least one of: a frame,one or more lenses or ear stems.